Re: An SSTC simulation

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Kchdlh-at-aol-dot-com 

As I see the operation of my "crossover control" circuit, I need the mutual 
coupling between the two secondaries to ensure that one transistor goes off 
before the other can be switched on.  Therefore, I need a separate 
transformer for each pair of transistors.  Connecting the emitters/sources 
together, via small resistors or not, would not be an option since each 
pair of transistors is to drive the t.c. primary thru its own 
series-resonating capacitor.

Separate series-resonating capacitors are to be used, of course, for 
failure-isolation: a short in one circuit shifts the resonant frequency & 
thus reduces the current in the other circuits.

As to big IGBTs...they're too slow, I believe.  (Correct me if I'm 
wrong.)  For sure, they're expensive; with paralleled smaller ones & 
separate resonating capacitors, I think failures could be isolated to the 
smaller/cheaper ones.

Regarding Jan Wagner's comment, I'm afraid I don't know much about 
soft-switching into a resonant load.  Nor how I might implement that while 
at the same time providing for frequency-control tied to the secondary's 
Fr--and at the same time keeping it all somewhere near  simple.

Ken Herrick



In a message dated 11/9/03 7:57:56 PM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>Subj:Re: An SSTC simulation
>Date:11/9/03 7:57:56 PM Pacific Standard Time
>From:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
>To:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
>Sent from the Internet
>
>
>
>Original poster: jimmy hynes <chunkyboy86-at-yahoo-dot-com>
>
>You don't really have to build 6 of the dual driver/crossover control
>circuits. You could use a
>gate drive transformer with 6 secondaries, or use big IGBTs, so you don't
>have to parallel them.
>You could also connect to the emitter through a 0.1 ohm resistor or
>something. The voltage should
>be pretty close, so the resistors should stay cool, and the current should
>share well.
>--- Tesla list <tesla-at-pupman-dot-com> wrote:
> > Original poster: Kchdlh-at-aol-dot-com
> >
> > 1.  The C8 voltage is 90 deg. out of phase with respect to the secondary
> > voltage.  C8 is, of course, the resonating capacitor rather than the
> > energy-storage capacitor; those are C4 & C7.
> >
> > 2.  The frequency is determined by my already-constructed secondary.  The
> > coupling coefficient I just picked out of the air; I can change it at will
> > in the simulation.
> >
> > 3.  If I actually get to building this I'll probably use IGBTs.  Partly so
> > I won't have to bother with Shottkys in series.
> >
> > 4.  The storage capacitors are the key to success: not too many (if any!)
> > will be expected to stand prolonged full-charge/full discharge at
> > 60/second.  I've queried Electrocube about their motor-run capacitors but
> > no response yet.
> >
> > In addition to repeating my comment that one would not need EX-OR U1, I'll
> > mention here that a mains-zero-crossing gate circuit should be added.  With
> > too much gain in E1, I found that oscillation tends to prolong so that
> > deleterious recharging of C4 or C7 will occur during the following 1/2
> > mains cycle.  You want to cut that off at 1-2 ms.  I've used another EX-OR
> > as a conventional pulse-generator running off the voltage across D5 and
> > operating a clamp-to-ground across D6/D7.
> >
> > I'll mention something else:  I now more fully realize that in any "totem
> > pole" power-transistor scheme using like-transistors (both N or both P),
> > and where you want to do as Terry Fritz has suggested in using multiple
> > resonating capacitors for paralleling the "totem poles", you have a problem
> > with driving all the "top" transistors--the ones with floating
> > sources.  Each has to be driven separately.  So...in my scheme, I'll have
> > to have 6 of the dual driver/crossover control circuits.  A bit of a
> > vexation but it can't be helped.
> >
> > Ken Herrick
> >
> >
> >
> > In a message dated 11/9/03 12:00:52 PM Pacific Standard Time,
> > tesla-at-pupman-dot-com writes:
> >
> >
> > >Subj:Re: An SSTC simulation
> > >Date:11/9/03 12:00:52 PM Pacific Standard Time
> > >From:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> > >To:<mailto:tesla-at-pupman-dot-com>tesla-at-pupman-dot-com
> > >Sent from the Internet
> > >
> > >
> > >
> > >Original poster: a a <hermantoothrot2000-at-yahoo-dot-com>
> > >
> > >Hi,
> > >
> > >In your simulations, does the voltage across C8 drop back to zero at the
> > >secondary voltage peak?
> > >
> > >I had thought about discharging the capacitor, but decided against it
> > >because the current it would have to withstand. You could get away with
> > >much less energy storage, which is good, but the rms current would be too
> > >high. In my current design, you can keep adding capacitors in 
> parrallel, so
> > >even cruddy capacitors will work if you have enough.
> > >
> > >Right now I have 40 1000uf 200v (10000uf 400v) capacitors for energy
> > >storage, but I think they may be the limiting factor in my design.
> > >
> > >The average driving voltage is also less, so you need a little more 
> current
> > >for the same power, but that is a minor point.
> > >
> > >I had also thought about dynamic tuning, but decided against it because of
> > >simplicity. It is very easy to manually find the resonant frequency if you
> > >are using an oscilloscope while it is running, but I don't know if you can
> > >do it otherwise. You still have to mess around with the tap point on the
> > >primary to get the right tuning there.
> > >
> > >Why such a high coupling and high frequency? You can get away with more
> > >transfer time, and it is easier on your MOSFETs. I used 8 cycles (K~0.12)
> > >at 60khz, and still got some pretty good results. I think IGBTs would be a
> > >better choice for this too. One IRG4PC40W would be better than your 6
> > >MOSFETs at any current above 35amps.
> > >
> > >If you find some capacitors that can stand completely discharging 60 times
> > >a second, then it would probably be a better way of doing things.
> > >
> > >[snipped]
> >
> >
>
>
>=====
>Jimmy
>